Processes for polymerizing acrylonitrile with starch are well known in the art. For example, such processes are shown in U.S. Pat. Nos. 2,922,768; 3,201,366; 3,661,815; 3,669,915; 3,935,099; 3,985,616; 3,997,484; 4,005,040; 4,045,387; and 4,069,177.
Most of these processes make use of starch (e.g., pearl starch) to produce a graft copolymer which forms a highly water absorbent polymeric composition. These starch-containing polymers can absorb water in amounts of 1,000 times or more by weight of water per weight of the polymeric composition. These products are highly useful in many applications including such uses as incorporation in disposable diapers, surgical pads and sheets, paper towels, disposable paper pads and the like.
The above-mentioned U.S. Pat. No. 4,045,387 discloses a process for producing a highly absorbent polymeric composition which is derived from flour such as corn or wheat flour. The process disclosed therein is purported to produce a product which will absorb from 1,800 to 3,000 times its weight of deionized water. It has been found that when corn flour or starch is used in the process of this patent to produce a polymeric composition, the polymeric composition will form a highly absorbent product consisting of discrete gel particles when contacted with such large amounts of water. That is, the polymeric composition consists of highly swollen gel particles which still maintain definite structural boundaries corresponding somewhat to the shape of the original particle prior to hydration.
Polymeric compositions which can absorb water in amounts of 5,000 to 10,000 times their weight of deionized water in the form of a soft gel in the absence of discrete particles would be highly desirable in certain applications, such as, for example as thickening and viscosity control agents for aqueous systems, and soil porosity control agents. It has been found impossible, however, to produce a soft gel from starch or corn flour utilizing the process of U.S. Pat. No. 4,045,387 which will absorb such large amounts of water. Similarly, it has also been found impossible to produce a soft gel from starch or corn flour utilizing the process of U.S. Pat. No. 3,997,484 which will absorb such large amounts of water.